The invention relates to a medication delivery device for delivering medicine or other fluent material into a mammal body.
Medication delivery devices are widely used in the health sector for delivering fluent medicine into mammal bodies through a conduit inserted in the body. In general two types of medication delivery devices exist. The first type being an injection device, which injects a selected dose of fluent medicine into a mammal body whenever the injection device is activated. The other type being an infusion device, which delivers a constant rate of medicine into a mammal body either by gravity or by pressure, which pressure are usually generated by an electrical motor.
People suffering from diabetes will require insulin to be delivered into the body either through several injections every day or through a constant infusion.
A medication delivery device for injecting pre-selected doses of fluent medicine into the body is known from WO 90.09202. The medication delivery device shown in this publication comprises a piston rod made up from an outer part and an inner part. The inner part has an exterior thread and is rotated by a drive mechanism. The outer part has an interior thread mating the thread of the inner part and is locked against rotation, such that the outer part moves forward whenever the inner part is being rotated. Since the outer part at its distal end abuts the elastomeric piston of the cartridge, this elastomeric piston is moved forward when the inner part is rotated hence expelling an amount of the medicine contained in the cartridge. In order to fully empty a cartridge the length of the outer part of the piston rod has to be at least equal to the length of the cartridge. The total length of the injection device must therefore be at least twice the length of the cartridge.
In order to produce medication delivery devices shorter than twice the length of the cartridge, a telescopic piston rod has been developed. Such a telescopic piston rod is shown, utilized in an infusion device, in WO 97.00091. This known piston rod comprises of a plurality of pieces or parts, which are connected to each other by mating threads. The distal part of the telescopic piston rod is connected to the elastomeric piston of the cartridge, and is prevented form rotating by a number of bushings surrounding the telescopic piston rod and being stiffly connected to the housing of the medication delivery device. When the drive rotates the proximal part of the telescopic piston rod, the distal part moves forward hence expelling the medicine contained in the cartridge.
If the shown telescopic piston rod has to fold and unfold correctly the bushing having the smallest diameter must surround the part of the telescopic piston rod having the largest diameter, as shown in WO 97.00091. The bushing having the smallest diameter then has to fit into at least one other bushing having a greater diameter, and finally the interior diameter of the cartridge has to be larger than the diameter of the largest bushing. As a result of this the diameter of the cartridge must be of a considerable size, especially if a long cartridge having a telescopic piston rod made up from a large number of parts is called for.
Another deficiency of the prior art medication delivery device is that the part of the largest bushing protruding out from the cartridge has to have an overall diameter equaling the interior diameter of the cartridge, leaving only a limited space in the housing for the remaining parts of the medication delivery device.
It is an object of the present invention to provide a medication delivery device, which does not posses the drawbacks of the prior art medication delivery devices, where the diameter of the cartridge is minimized, and where the non-occupied space available inside the housing is maximized.
This is obtained by a medication delivery device for delivering medicine or other fluent material to a mammal body, having a housing accommodating a cartridge containing an amount of said medicine, comprising:
an elastomeric piston movable mounted in said cartridge, which elastomeric piston is moved from a proximal end of said cartridge to a distal end of said cartridge by rotating at least a part of a first telescopic piston rod, which first telescopic piston rod has a distal part abutting said elastomeric piston and a proximal part rotatably mounted in said housing and a plurality of parts there between, said parts being connected to each other by mating threads,
drive means for rotating said first telescopic piston rod, such that said elastomeric piston moves forward inside said cartridge and expels an amount of said medicine, and
means preventing said elastomeric piston from rotating when said part of said first telescopic piston rod is rotated,
which medication delivery device according to the invention is characterized in that
said means preventing said elastomeric piston from rotating when at least a part of said first telescopic piston rod is rotated comprises an additional telescopic piston rod having a proximal end mounted in said housing and a distal end abutting said elastomeric piston.
When a telescopic piston rod is used, the elastomeric piston most be prevented from rotating in order to be advanced inside the cartridge. If an additional piston rod abutting the elastomeric piston is located in the cartridge this will effectively hinder the elastomeric piston from rotating when the first piston rod is expanded. Both piston rods can be made with a very little diameter, such that they both at the same time can fit into the interior of a standard cartridge. Since they are both fitted into the same cartridge, the addition of the diameter of both the telescopic piston rods is substantially smaller than the interior diameter of the cartridge, thereby leaving some non-occupied space both in the cartridge and in the housing of the medication delivery device.
In the present context the term xe2x80x98elastomeric pistonxe2x80x99 is taken to mean a displaceable plate or cylinder that fits tightly to the inner walls of a cartridge. One surface of the elastomeric piston is in contact with the contents of the cartridge while the opposite surface is in contact with a piston rod.
The term xe2x80x98piston rodxe2x80x99 is in the present context taken to be the element which are used to apply pressure to a surface of the elastomeric piston, such that the elastomeric piston is being displaced and the contents of the cartridge is being expelled.
The term xe2x80x98telescopic piston rodxe2x80x99 is taken to mean a piston rod made up from a number of individual parts or pieces, which parts or pieces preferably has a circular cross-section, but the parts could if wanted be of any desired form. All the pieces, although the most distal part or piece could be solid, is preferably hollow thereby creating an interior compartment in each part or piece, which compartment has a diameter or a width large enough to fit the neighbouring piece into the compartment, such that the telescopic piston rod can be transformed from a position where all the pieces are contained in the compartment of the neighbouring piece to a position where all the pieces are extracted out of the compartments or almost of the compartments. In the first position the overall length of the telescopic piston rod is somewhat equal to the length of the longest part or piece, and in the extracted position the length of the telescopic piston rod almost equals the total sum of the length of each individual piece.
In the present context, the term xe2x80x98abutting the elastomeric pistonxe2x80x99 or xe2x80x98elastomeric piston . . . in contact with a piston rodxe2x80x99 is taken to mean that the piston rod may or may not be fixed to the movable elastomeric piston. In both cases the piston rod has the ability to displace the elastomeric piston at least in a direction towards the outlet of the cartridge. When, as disclosed in claim 2, the additional telescopic piston rod is rotatably mounted in the housing, it is ensured that a telescopic piston rod equal to the first telescopic piston rod can be utilized as the additional telescopic piston rod.
When, as disclosed in claim 3, the additional telescopic piston rod extends parallel with the first piston rod inside said cartridge, it is ensured that the construction of the bearings can be kept simple. The bearings carrying the rotating parts of the telescopic piston rods can e.g. be ball bearings as shown or a combination of a ball bearing and a needle bearing located at the proximal end of the telescopic piston rod. If the two telescopic piston rods crosses each other inside the cartridge, or if they in any other way are kept non-parallel, the design of the bearings will be much more complicated.
When, as disclosed in claim 4 the first telescopic piston rod and said additional telescopic piston rod is connected to each other through a synchronisation gear such that both telescopic pistons rods rotates with the same rotational speed, and that one of said telescopic piston rods is rotated by an electrical motor which drives one of said telescopic piston rod through a driving gear, it is ensured that although the electrical motor only drives one of the two telescopic piston rods they are both rotated with the same rotational speed. If the pitch of the threads connecting the pieces of each telescopic piston rod is the same for both telescopic piston rods it is ensured that the distal end of each telescopic piston rod moves at the same speed. If the synchronization utilizes only two gear wheels, as shown, the first telescopic piston rod and the additional telescopic piston rod will rotate in different directions. When the two telescopic piston rods are moving in different directions, the momentum delivered to the elastomeric piston from the one telescopic piston rod being driven by the electrical motor will be equalized by the momentum delivered from the other telescopic piston rod and the resulting momentum working on the elastomeric piston will be zero. If an uneven number of gearing wheels are utilized, the two telescopic piston rods will rotate in the same direction which will build up a momentum at the point where the telescopic piston rods is secured in the housing.
In an embodiment of the medication delivery device according to the invention, the first telescopic piston rod and said additional telescopic piston rod each comprises of three parts; a first part having an interior thread, a third part having an exterior thread and an intermediate second part having an exterior thread mating said interior thread of said first part and an interior thread mating said exterior thread of said third part. Having a telescopic piston rod made up from three parts have been found to provide a length and a stability suitable for a medication delivery device
When, as disclosed in claim 6, the first part of said first telescopic piston rod and said first part of said additional telescopic piston rod is located at said proximal end of said cartridge, and that said third part of said first telescopic piston rod and said third part of said additional telescopic piston rod is moving towards said distal end of said cartridge, it is ensured that the piece of each telescopic piston rod having the largest diameter and containing the other pieces of the telescopic piston rod is the piece located at the most proximal end of the medication delivery device.
The direction of the pith of the threads provided on the pieces making up each telescopic piston rod determines in which direction each telescopic piston rod moves when the first piece is being rotated. In an embodiment of the medication delivery device according to the invention, the direction of said threads of said first telescopic piston rod and said additional telescopic piston rod is such that said distal end of each telescopic piston rod travels in the same direction inside said cartridge when one of said telescopic piston rods is rotated. If as mentioned in claim 8, the first telescopic piston rod and said additional telescopic piston rod rotates in the same direction, the threads of each telescopic piston rod most be in the same direction whereas if the first telescopic piston rod and said additional telescopic piston rod rotates in opposite directions, as mentioned in claim 9, the thread of each telescopic piston rod most be in opposite directions.
When, as disclosed in claim 10, the first telescopic piston rod at said distal end is connected to said distal end of said additional telescopic piston rod preferably through a circular plate abutting said elastomeric piston inside said cartridge, it is ensured that the two telescopic piston rods are locked to each other and that the momentum is adequate balanced between the two telescopic piston rods.